El-Sayed would have been the first Muslim governor in the U.S. if elected this year, according to NBC.

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Stewart said the tweet was sent from a vendor and that as soon as he saw it, he took it down. He added that his campaign terminated the individual's Twitter access as a result, but did not discipline the person any further.

"One of my vendors put out a tweet last night that attempted to link a Michigan gubernatorial candidate to ISIS, because he apparently received support from purported extremists," Stewart said in a statement to The Hill. "I don't believe in guilt by association. I have been the target of very similar smears, and I don't believe in using such tactics against others."

Stewart has been a controversial figure in Virginia politics for alleged ties to white nationalists and his past defense of Confederate monuments.